The overall goals of the research project administered through the South Dakota Health Research Foundation are to define the frequency of breast cancers from American Indian patients that express a novel tumor marker designated BASE and to investigate overexpression of HER2 in breast cancers isolated from American Indian females. This information will determine whether BASE and HER2 are useful breast cancer tumor markers in American Indians. This research will explore the presence of a newly discovered tumor marker, BASE, and amplification of a clinically validated marker, HER2, in breast cancers from Native American women. The knowledge gained from this proposal will advance our understanding of whether BASE could be used as a tumor marker for breast cancer in American Indian women. In addition, we will begin to determine the status of HER2 overexpression in breast cancers from American Indians. In order to accomplish these goals, I propose the following specific aims: Specific Aim 1. Determine frequency and types of breast cancers from American Indian women that express BASE. Specific Aim 2. Investigate the status of HER2 amplification in breast cancers from American Indian women. One long-term goal of this research program is to validate whether the Esr1, Pgr, BRCA1, BRCA2 and the extent of HER2 amplifications accurately predict treatment and overall survival of American Indian females with breast cancer. This pilot project will give us the opportunity to begin to investigate the status of HER2 amplification in American Indian breast cancers. In the future, it will also be necessary to analyze the status of the Esr1 and Pgr in the same samples.